A detector system of this type is described, for example, in European Published Patent Application No. 0 250 711, which is used in the scanning unit of an optical position-measuring device to scan a periodic fringe pattern, which results in a detection plane there. The fringe pattern is produced in a conventional manner on the basis of the interaction of the light bundle, emitted by a light source in the scanning unit, with a measuring graduation and, if applicable, one or more further graduations in the scanning beam path. If the scanning unit and the measuring graduation move relative to each other, the fringe pattern is shifted perpendicular to the fringes and therefore is periodically intensity-modulated at each position. From the optoelectronic scanning of the fringe pattern, displacement-dependent, sinusoidal scanning signals may be generated in a conventional manner in the form of periodic incremental signals. As a rule, two or more incremental signals are phase-shifted in a defined manner and are then further processed in sequential electronics are generated in this manner.
Because of the wide variety of interference effects, as a rule the scanning signals generated in this manner are not ideally sinusoidal, but rather, because of harmonic components, have a signal shape deviating therefrom. However, for error-free further processing of the scanning signals in sequential electronics, signals which, to the greatest extent possible, are free of harmonics are desirable. For this reason, European Published Patent Application No. 0 250 711 proposes carrying out a defined harmonic filtering by a suitable arrangement and dimensioning of the individual detector elements in the detector system provided. To that end, widely varying geometrical shapes of the individual detector elements are proposed in various exemplary embodiments. Disadvantageous in the various design approaches, however, is that, first of all, the available detector-element surface area is not fully utilized, thus certain regions of the detector-element surface area remain unused. However, for a high signal intensity, the best possible utilization of the available detector-element surface area is desirable. Secondly, the proposed geometries of the detector elements are sensitive to possible interferences in the scanned fringe pattern, which in turn can lead to signal errors. Such interferences in the fringe pattern may be caused, for instance, by tilting and/or rotating the scanning unit with respect to the measuring graduation, or else by an uneven surface of the measuring graduation. The result in these cases are deformed and/or stretched fringe patterns which are scanned.
It is an aspect of the present invention to provide an optoelectronic detector system for a scanning unit of an optical position-measuring device that may ensure both reliable harmonic filtering in the resulting scanning signals, as well as an efficient utilization of the available detector surface possible.